The present invention relates to asynchronous sampling digital detection (ASDD) methods and apparatus.
Auxiliary storage devices, such as ones used in connection with computers, are usually based upon moving memory devices such as rotating magnetic or optical disks and drums, or upon moving magnetic tape, which may be locally, physically altered in magnetic or optical properties to represent data. Locations for physically altered regions are aligned and spaced in tracks to ease location and read back of the data represented by the regions. Ideally, as a track is moved passed a read back transducer at a fixed speed, the locations are presented at regular intervals and the physically altered regions are appropriately aligned and spaced to allow generation of equally and evenly spaced electrical pulses for formatting as data.
The conditions of data storage and recovery are rarely ideal and, as a result, data recovery channels must be adapted to overcome difficulties in detecting encoded binary information. In retrieving data from a storage system, a read channel is typically utilized to convert the data into a digital format. In a magnetic tape system, data is sensed by a read head and transformed into an analog signal. The analog signal may be amplified and filtered. The signal is then sampled and converted into a digital signal by an analog-to-digital converter.
One type of system for data recovery employs peak detection to retrieve encoded binary information. In a peak-detection system, a peak detector is employed in a read channel to aid in detecting logical ones and zeros in the digital signal. Binary information is encoded within the digital signal. The peak detector recognizes logical ones and zeros by locating the peaks of a waveform. The peak detector interprets a peak as a logic one. The distance between peaks can be utilized to encode binary information such as representing zeros. Accordingly, accurate detection of the distance between peaks can be very important in accurately detecting the encoded information.
Noise, however, can affect the manner in which digital data is interpreted. Specifically, noise can muddle the detection process such that the distance between peaks is not detected in the form of an integer value (which can be most desirable), but rather as an integer plus some fractional component which is indicative of, or caused by noise which is present in the system.
One solution which has been proposed to address such noise-corrupted information has been to simply round the received integer and fractional component to the nearest integer. Thus, in systems where a noise component constitutes less than 0.5, the rounded integer would accurately describe the correct digital data. However, in systems where the noise component contributes 0.5 or more, the system would inaccurately round to a next higher integer, thereby inaccurately detecting the encoded binary information.
Asynchronous Sampling Digital Detection, or ASDD systems and methods can be used to retrieve data such as that described above. Various aspects of ASDD methods and apparatus are described in U.S. Pat. Nos. 5,293,369, 5,629,914, 5,461,642, 5,295,128, 5,442,315, 5,461,638, 5,315,284, 5,530,601, and 5,502,711, the disclosures of which are incorporated by reference herein.
This invention arose out of concerns associated with improving ASDD methods and apparatus.
Asynchronous Sampling Digital Detection (ASDD) methods and apparatus are described. In one embodiment, noise-corrupted information is received and comprises a plurality of information-carrying events which encode binary information which is desired to be retrieved. A plurality of values are extracted from the noise-corrupted information-carrying events which are representative of the encoded binary information. An amount of noise corruption carried by one of these plurality of values is estimated by considering an amount of noise corruption carried by another of the plurality of values. Responsive to the estimation of the noise corruption, the one value is then modified. In another embodiment, noise-corrupted information is received comprising a plurality of information-carrying events which encode binary information which is desired to be retrieved. A plurality of values from the noise-corrupted information-carrying events are determined which are representative of the encoded binary information. A set of conditions is defined which are a function of the plurality of values, and which have value-dependent outcomes. For a given determined value of the plurality of values, a value-dependent outcome is imposed to produce at least two intermediate noise-adjusted values. Using the two intermediate noise-adjusted values, a noise-reduced output value for the given determined value is selected.